Various techniques for removing oxygen from dry food containers are known in the art. Such containers are used, for example, for the packaging of nuts, coffee, powdered milk, cheese puffs, and various other dry foods. Typically, these containers are exposed to an inert gas flush and/or vacuum for a period of time, subsequent to filling but prior to sealing. When the oxygen has been substantially removed from the food contents therein, the containers are sealed, with or without vacuum.
A gas flushing apparatus for removing oxygen from food containers is disclosed in U.S. Pat. No. 4,140,159, issued to Domke. A conveyor belt carries the open top containers in a direction of movement directly below a gas flushing device. The gas flushing device supplies inert gas to the containers in two ways. First, a layer or blanket of low velocity flushing gas is supplied to the entire region immediately above and including the open tops of the containers through a distributing plate having a plurality of small openings. Second, each container is purged using a high velocity flushing gas jet supplied through a plurality of larger jet openings arranged side-by-side in a direction perpendicular to the direction of movement of the food containers. As the containers move forward, in the direction of movement, the steps of inert gas blanketing followed by jet flushing can be repeated a number of times until sufficient oxygen has been removed from the containers, and from the food contents therein.
One aspect of the apparatus disclosed in Domke is that the flow of gas in a container is constantly changing. As a container moves past a high velocity jet of flushing gas, the jet is initially directed downwardly into the container at the leading edge of the container open top. As the container moves further forward, the flushing gas is directed into the center and, later, into the trailing edge of the open top, after which the container is no longer exposed to that particular jet. Then, the process is repeated as the container passes below another jet.
Constantly changing jet patterns in prior art devices create turbulence above and within the containers, which can cause surrounding air to be pulled into the containers by the jets as well as removed. This turbulence imposes a limitation on the speed at which the containers pass below the jets. As the containers move faster beneath the jets, the flow patterns within the containers change faster, and the turbulence increases. Also, at high line speeds, purging gas has more difficulty going down into the containers, and a greater tendency to remain in the head space above the containers. Also, a perpendicular arrangement of jets relative to the direction of container travel causes much of the jet to be directed outside the containers, especially when the containers are round.